Moccasin Dam holds steady, could still fail in Tuolumne County

TULOUMNE COUNTY, Calif. (KGO) -- A dam just west of Yosemite is holding steady. Earlier this afternoon, authorities warned it's likely it would fail. It did cause flooding in Tuolumne County.

On Thursday afternoon, the California Fish and Wildlife Trout hatchery flooded in Tuolumne County. Workers there were evacuated. The water came rushing down from the Moccasin Reservoir Dam. The sheriff's department went into emergency mode because water authorities advised the dam would likely fail after heavy rain saturated the area. State Route 49 remains closed at State Route 120 because floodwaters washed out part of the road.

Doctor Sukhmander Singh teaches Civil Engineering at Santa Clara University. He says this particular dam was built in 1930 and point out the majority of California's dams were built before 1970 and were made of compacted earth.

But Singh says many of the construction records for the older dams don't exist so it's unknown how well the dirt was compacted.

"Sustained rainfall for long period bring runoff that means there's a possibility it may overflow, spillway may be overtaxed, overworked," explained Singh.

The dam is stable for now.The San Francisco Public Utilities Commission is monitoring the situation and says the spillway is damaged.

Everything will be inspected. The flood waters were contained by the Don Pedro Reservoir, a mile downstream.

The reservoir is part of the Hetch Hetchy water system that provides millions of gallons of water to San Francisco, the Peninsula, and Santa Clara. Officials say our water supply in the Bay Area was not affected.

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